U.S. patent number 5,410,884 [Application Number 08/137,343] was granted by the patent office on 1995-05-02 for combustor for gas turbines with diverging pilot nozzle cone.
This patent grant is currently assigned to Mitsubishi Jukogyo Kabushiki Kaisha. Invention is credited to Ichiro Fukue, Tetsuo Gora, Hitoshi Kawabata, Shigemi Mandai, Hiroyuki Nishida, Nobuo Sato, Katsunori Tanaka.
United States Patent |
5,410,884 |
Fukue , et al. |
May 2, 1995 |
Combustor for gas turbines with diverging pilot nozzle cone
Abstract
A gas turbine combustor suppresses the generation of NOx by
mixing a fuel and air homogeneously. A pilot nozzle is provided at
the center of the gas turbine combustor. A plurality of main
nozzles surround the pilot nozzle. A diverging cone projects from
the vicinity of the injection port of the pilot nozzle such that
the flame from the main nozzles is sustained by the pilot nozzle
and NOx is suppressed. The main nozzles can be provided upstream of
the injection port of the pilot nozzle in which case an annular
premixing nozzle having a throttled exit end is disposed downstream
of the main nozzles. The main nozzle may also be in the form of a
fuel nozzle having a plurality of tubes, a gaseous fuel being
injected through one of the tubes, and liquid fuel being injected
into the annular premixing nozzle through the other of the tubes so
that the liquid fuel is atomized to mix the fuel and air
homogeneously.
Inventors: |
Fukue; Ichiro (Takasago,
JP), Mandai; Shigemi (Takasago, JP),
Tanaka; Katsunori (Takasago, JP), Kawabata;
Hitoshi (Takasago, JP), Sato; Nobuo (Takasago,
JP), Nishida; Hiroyuki (Takasago, JP),
Gora; Tetsuo (Takasago, JP) |
Assignee: |
Mitsubishi Jukogyo Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
26387389 |
Appl.
No.: |
08/137,343 |
Filed: |
October 18, 1993 |
Foreign Application Priority Data
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Oct 19, 1992 [JP] |
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4-304442 |
Feb 12, 1993 [JP] |
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5-047227 |
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Current U.S.
Class: |
60/267;
60/259 |
Current CPC
Class: |
F23D
17/002 (20130101); F23R 3/286 (20130101); F23R
3/34 (20130101); F23R 3/36 (20130101); F23D
2205/00 (20130101) |
Current International
Class: |
F23R
3/36 (20060101); F23R 3/28 (20060101); F23R
3/34 (20060101); F23D 17/00 (20060101); F02C
001/00 () |
Field of
Search: |
;60/746,737,748,742,733,740,747,39.06,749 ;239/405,406 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0095788 |
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Dec 1983 |
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EP |
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0108361 |
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May 1984 |
|
EP |
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0269824 |
|
Jun 1988 |
|
EP |
|
0455487 |
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Nov 1991 |
|
EP |
|
0564184 |
|
Oct 1993 |
|
EP |
|
654122 |
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Jun 1951 |
|
GB |
|
Primary Examiner: Bertsch; Richard A.
Assistant Examiner: Wicker; William J.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What is claimed is:
1. A gas turbine combustor comprising: a combustion chamber; a
pilot nozzle disposed on the axial centerline of the gas turbine
combustor upstream of said combustion chamber, said pilot nozzle
having an injection port; a cone projecting from the vicinity of
the injection port of said pilot nozzle, the cone having a diverged
base end adjacent the combustion chamber; a plurality of main
nozzles disposed around said pilot nozzle, each of said main
nozzles having a fuel injection portion defining an injection port
and a respective primary mixing chamber wall surrounding the fuel
injection portion to form a primary mixing chamber in the main
nozzle; and a secondary mixing chamber, located between the primary
mixing chamber wall of each of said main nozzles and said end of
the cone, in which air and a fuel/air mixture from said main
nozzles are mixed before passing to the combustion chamber, said
secondary chamber being delimited and throttled by said end of the
cone.
2. A gas turbine combustor according to claim 1,
wherein said plurality of main nozzles are disposed upstream of the
injection port of said pilot nozzle,
and said secondary mixing chamber comprises an annular premixing
nozzle having a throttled exit end adjacent said combustion
chamber.
3. A gas turbine combustor according to claim 2,
wherein each of said main nozzles includes at least first and
second tubes, the first tube having an injection port within the
primary mixing chamber wall such that gaseous fuel is fed through
the first tube within the primary mixing chamber wall of said main
nozzle, and the the second tube having an atomizer at the exit end
of said annular premixing nozzle.
4. A gas turbine combustor according to claim 1, and further
comprising vanes extending inwardly from the primary mixing chamber
wall of each of said main nozzles.
5. A gas turbine combustor according to claim 2, and further
comprising vanes extending inwardly from the primary mixing chamber
wall of each of said main nozzles.
6. A gas turbine combustor according to claim 3, and further
comprising vanes extending inwardly from the primary mixing chamber
wall of each of said main nozzles.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustor capable of reducing
NOx in a gas turbine.
2. Description of the Relevant Art
The entrance temperature of a gas turbine has been elevated in
recent years to obtain higher efficiencies in cogenerator plants
which tends to result in an increase in the generation of NOx.
Serious demands for lower NOx content in the exhaust gases have
thus been raised and met by various proposals.
One of the factors influencing-the amount of NOx produced is the
combustion temperature, and it is known that the lower the
combustion temperature the less NOx is generated. At present,
therefore, a two-stage combustion system has been developed to
effect efficient combustion and to suppress the rise of the
combustion temperature and accordingly the generation of NOx. In
this two-stage combustion system, diffusion combustion is performed
at the first stage for obtaining ignition and flame stability, and
premixed combustion is performed at the second stage to obtain a
high NOx reducing effect.
FIG. 10 shows a premixed type of combustor for a gas turbine in the
prior art. In FIG. 10, a gas turbine premixed type of combustor 01
has a pilot nozzle 02 at its center. A plurality of cylindrical
main (or premixing) nozzles 03 are disposed along a common circle
around the pilot nozzle 02. In this arrangement, each main nozzle
03 has its leading end located substantially in the same plane as
that of the leading end of the pilot nozzle 02. Incidentally,
reference numeral 04 designates a combustion chamber, and numeral
05 designates swirl vanes.
As described above, as the entrance temperature of the gas turbine
rises, the more NOx is emitted to the atmosphere. This raises
serious demands for a system producing a lower amount of NOx in the
exhaust gases. Because the rise in gas temperature increases the
amount of the air burnt, the mixing of the fuel and air is an
important factor which has been investigated in reducing the NOx
content of the exhaust gas.
In the premixed type of combustor of the prior art shown in FIG.
10, however, the premixing nozzles collectively constitute a
cylindrical structure with the aim of achieving a compact combustor
structure. Thus, the mixing of the fuel and air does not always
sufficiently limit the generation of NOx.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the aforementioned
problems of the prior art by providing a gas turbine combustor
which minimizes the generation of NOx by promoting the mixing of
the fuel and air.
In order to achieve the above object, the present invention
provides a gas turbine combustor comprising: a combustion chamber;
a pilot nozzle arranged at the center of the gas turbine combustor;
a plurality of main nozzles arranged around the pilot nozzle and
each forming a primary mixing chamber; a diverging cone projecting
from the vicinity of the injection port of said pilot nozzle toward
the combustion chamber; and a secondary mixing chamber between the
primary mixing chamber and the end of the cone (the combustion
chamber).
The plurality of main nozzles may be provided upstream of the
injection port of the pilot nozzle, wherein the secondary mixing
chamber is an annular premixing nozzle having a throttled exit
end.
Further, each of the main nozzles may be in the form of a fuel
nozzle having at least two tubes, one for injecting gaseous fuel
within the primary mixing wall of the main nozzle and the other for
atomizing a liquid fuel at the exit end of the annular premixing
nozzle.
The diverging cone projects from the vicinity of the injection port
of the pilot nozzle so that the zone of the circulating flow of the
fuel downstream of the pilot nozzle is comparatively large to
enhance the ability of the main flame to be maintained by the pilot
flame (flame stability). As a result, the combustion is stable even
at a low pilot injection rate producing a correspondingly low
amount of NOx.
Further, the fuel and air are mixed in individual doses in the
plurality of main nozzles arranged around (and preferably upstream
of) the pilot nozzle, and the mixtures then join and are mixed in
the secondary mixing chamber (the annular premixing nozzle) so that
the air and fuel are further homogeneously mixed to improve their
combustion in the combustion chamber to reduce the generation of
NOx. Moreover, the homogeneous mixture is introduced at a high
velocity into the combustion chamber through the throttled exit end
of the annular premixing nozzle so that flash-back can be prevented
while enhancing flame stability.
With the fuel nozzle of the invention, the gaseous fuel is injected
into the main nozzles, and the liquid fuel is sprayed at the exit
end of the annular premixing nozzle, so that the fine liquid vapors
are evaporated and premixed with the gaseous fuel. As a result, the
liquid fuel is homogeneously gasified to ensure combustion having a
low NOx content.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of a first embodiment of a
combustor according to the present invention;
FIG. 2 is a longitudinal sectional view of a second embodiment of
the present invention;
FIG. 3 is a diagram illustrating the fuel concentration
distribution at the nozzle exit of the second embodiment of the
combustor;
FIG. 4 is a diagram illustrating the fuel concentration
distribution at the nozzle exit of the premixed type of combustor
of the prior art;
FIG. 5 is a graph plotting NOx concentrations from combustion tests
of the second embodiment of the premixed type of combustor;
FIG. 6 is a graph plotting the NOx concentrations from combustion
tests of the premixed type of combustor of the prior art;
FIG. 7 is a longitudinal sectional view of a third embodiment of
the present invention;
FIG. 8 is a graph comparing NOx emissions of the third embodiment
and the prior art;
FIG. 9(a) is a longitudinal sectional view of a fuel nozzle of a
fourth embodiment of the present invention, and FIG. 9(b) is a
cross-sectional view of the same; and
FIG. 10 is a longitudinal sectional view of a premixed type of
combustor of a gas turbine of the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will be described in
the following with reference to FIG. 1. In FIG. 1, a combustor 1
has, at its center, a pilot nozzle 3 directed toward the combustion
zone of an inner cylinder 2. The pilot nozzle 3 is surrounded by a
plurality of main nozzles 4. These main nozzles 4 are arranged such
that the ends of their injection ports 4a lie in generally the same
plane as that in which the end of the injection port of the pilot
nozzle 3 lies. Reference 4b designates a primary mixing chamber
wall of the main nozzle.
A diverging cone 5 projects from the injection port of the pilot
nozzle 3. The diverging cone 5 is also directed toward the
combustion zone of the inner cylinder 2, to expand the zone of the
circulating flow of a fuel injected from the pilot nozzle 3. As a
result, a stable combustion can be established even at a low
injection rate of the pilot fuel, to reduce the emission of NOx
from the pilot nozzle 3. Incidentally, reference numeral 6
designates the fuel pipe of the main nozzles 4.
A second embodiment of the present invention will be described with
reference to FIGS. 2 to 6.
In FIG. 2, a premixed type of gas turbine combustor 11 has a pilot
nozzle 12 at the center thereof. The combustor 11 also includes a
plurality of cylindrical main (or premixed) nozzles 13 disposed
around the pilot nozzle 12 in a common circle. These main nozzles
13 are shorter than the main nozzles 03 of the prior art shown in
FIG. 10 and are located upstream of the pilot nozzle 12. Each of
the main nozzles 13 has swirl vanes 15. An annular premixing nozzle
16 extends downstream of the cylindrical main nozzles 13. As a
result, the insides of each of the cylindrical main nozzles 13
provide primary mixing chambers for the fuel and air, and the
inside of the annular premixing nozzle provides a secondary mixing
chamber. The secondary mixing chamber has an inner circumference
defined by an inner cylinder 17, which has its exit end 18 diverged
or expanded radially outward toward a downstream combustion chamber
14 so that the premixture flow passage is converged or
throttled.
The operation of the second embodiment of the combustor will be
described. The fuel and air are mixed at a first stage in the
cylindrical primary mixing chambers of the main nozzles 13, and
these preliminary mixtures join one another and are subjected to a
second-stage mixing in the annular premixing nozzle 16 so that the
fuel and air are sufficiently mixed into a homogeneous mixture.
Thus, the combustion in the combustion chamber 14 generates a
comparatively low amount of NOx.
On the other hand, the flow velocity of the mixture is accelerated
when it flows into the combustion chamber 14 due to the fact that
the secondary mixture chamber is throttled by the diverging exit
end 18 of the inner cylinder 17 defining the inner circumference of
the annular premixing nozzle (secondary mixing chamber) 16. As a
result, flash-back can be prevented, and the circulating flow can
be formed without fail at the diverging exit end 18 of the inner
cylinder 17 to ensure flame stability.
FIG. 3 is a diagram plotting fuel concentration distributions at
the nozzle exit of the premixed type of combustor according to the
present invention, as shown in FIG. 2, and FIG. 4 is a diagram
plotting fuel concentration distributions at the nozzle exit of the
premixed type of combustor of the prior art, as shown in FIG. 10.
In FIGS. 3 and 4, moreover, letter x designates the distances from
the confluences at which the mixture from the pilot nozzle and the
mixtures from the main nozzles join one another. As can be seen by
comparing those figures, the premixed type of combustor of the
prior art has a wide-ranging fuel concentration distribution at the
nozzle exit. In the premixed type of combustor according to the
present invention, on the contrary, the mixtures from the main
nozzles have substantially homogeneous fuel concentrations at the
confluence.
On the other hand, FIG. 5 is a graph plotting the NOx
concentrations which were obtained from combustion experiments
carried out on the premixed type of combustor according to the
present invention, as shown in FIG. 2, and FIG. 6 is a graph
plotting the NOx concentrations which are obtained from combustion
experiments carried out on the premixed type of combustor of the
prior art, as shown in FIG. 10. In FIGS. 5 and 6, moreover, the
solid curves join points which were determined as yielding the best
results including with respect to CO concentrations. The comparison
of these figures will reveal that the present invention can reduce
the NOx concentrations to one half of that in the prior art under
the rated load conditions, as indicated at points A.
A third embodiment of a dual-fuel burning premixed type of
combustor according to the present invention will be described with
reference to FIG. 7. In this embodiment, the pilot nozzle 12, the
main (or premixing nozzles) 13, the swirl vanes 15, the annular
premixing nozzle 16, the inner cylinder 17, and the exit end of the
inner cylinder are all of the same structures as those of the
foregoing second embodiment.
A plurality of fuel nozzles 24 for feeding individual jets of fuel
within the primary mixing walls of the main nozzles 13 and into the
annular premixing nozzle 16 extend through the main nozzles 13 and
the annular premixing nozzle 16. Leading ends of the fuel nozzles
24 located at the exit end of the premixing nozzle 16 are directed
downstream of the premixed combustor 21.
These fuel nozzles 24 each comprise two tubes, one of which is fed
with gaseous fuel (to constitute part of a main nozzle) whereas the
other is fed with liquid fuel. That is, the gaseous fuel is
injected through an injection part of the first tube just
downstream of the swirl vanes 15 within primary mixing walls of the
cylindrical main nozzles 13 so that it is preliminarily mixed with
the swirls by the swirl vanes 15 and then injected downstream. The
resultant mixture jets atomize the fine liquid fuel vapors, which
are sucked and vaporized from the second tube of the fuel nozzles
24 at the exit end of the annular premixing nozzle 16, into a finer
and more homogeneous mixture. In short, the fine fuel vapors are
preliminarily evaporated and mixed sufficiently with the gaseous
fuel so that they are completely burned whereby the resulting
combusted fuel has a low NOx concentration.
FIG. 8 compares the generation of NOx of the combusted fuel
generated in the third embodiment of the dual-fuel burning premixed
type of combustor according to the present invention, as shown in
FIG. 7, and that generated in the premixed type combustor of the
prior art, as shown in FIG. 10. The generation of NOx from the
gaseous fuel an the liquid fuel are plotted when the individual
combustors are run under predetermined loads. For the liquid fuel
(or oil), it is found that the combustor of the present invention
always generates combusted fuel having a NOx concentration as low
as about 50% of that of the combusted fuel generated in the
conventional combustor. For the gaseous fuel, on the other hand,
the combustor of the present invention generates combusted fuel
having about 50% of the NOx content of the prior art under a light
load, and about 20% under a high load.
A fourth embodiment of the present invention will be described with
reference to FIGS. 9(a), 9(b). In the present embodiment, the dual
fuel nozzles 24 of the foregoing third embodiment are replaced by
triple fuel nozzles 34, as will be described in the following.
Specifically, each triple fuel nozzle 34 is constructed of three
tubes: the innermost one providing a liquid fuel passage 34a for
the liquid fuel, the outermost one providing an air passage 34b for
the air, and the intermediate one providing a gaseous fuel passage
34c for the gaseous fuel. The intermediate gaseous fuel passage 34c
extends downstream of the swirl vanes 15 of the main nozzle 13 so
that the gaseous fuel may be injected into the main nozzle 13
through radially formed tubular passages 35 constituting an
injection port of the main nozzle 13. On the other hand, the
innermost liquid fuel passage 34a and the outermost air passage 34b
extend together to the vicinity of the injection port of the fuel
nozzle 34.
In the present embodiment, the gaseous fuel is injected from just
behind the swirl vanes 15, as indicated by arrow, into the
cylindrical main nozzle 13 and is premixed with the air flows by
the swirl vanes 15 so that this preliminary mixture is injected
into the annular premixing nozzle 16 located downstream thereof. On
the other hand, the liquid (or oil) fuel is injected by the
two-fluid or air/oil nozzle for atomizing with the air, so as to
promote the mixing, i.e., to make the injected vapors finer and
more homogeneous.
The liquid fuel passage 34a and the air passage 34b extend to the
vicinity of the injection port of the fuel nozzle 34 so that the
liquid fuel is atomized at the exit end of the fuel nozzle 34,
which is disposed at the injection port of the annular premixing
nozzle 16, by the air flow injected from the air passage 34b. At
this time, the air flowing from the air passage 34b acts to promote
the vaporization of the liquid fuel and atomize the fuel vapors.
The gaseous fuel premixed in the cylindrical main nozzles 13 is
injected to promote the atomization of the atomized liquid fuel so
that the fuel is homogenized to ensure a complete fuel combustion
and low NOx emission.
According to the aforementioned third and fourth embodiments, the
fuels can be prevented from overheating by the multiplex fuel
passages. According to the fourth embodiment, moreover, this fuel
cooling effect is enhanced by the air passage disposed at the
outermost side.
* * * * *